The demand for coniferous trees, such as pines and firs, to make wood products continues to increase. One proposed solution to this problem is to identify individual trees that possess desirable characteristics, such as a rapid rate of growth, and produce numerous, genetically identical, clones of the superior trees by somatic cloning.
Somatic cloning is the process of creating genetically identical trees from tree tissue other than the male and female gametes. In one approach to somatic cloning, plant tissue is cultured in an initiation medium which includes hormones, such as auxins and/or cytokinins, that initiate formation of embryogenic cells that are capable of developing into somatic embryos. The embryogenic cells are then further cultured in a maintenance medium that promotes multiplication of the embryogenic cells. The multiplied embryogenic cells are then cultured in a development medium that promotes development of conifer somatic embryos which can, for example, be placed within artificial seeds and sown in the soil where they germinate to yield conifer seedlings. The seedlings can be transplanted to a growth site for subsequent growth and eventual harvesting to yield lumber, or wood-derived products.
A continuing problem with somatic cloning of conifer embryos is stimulating efficient formation of conifer somatic embryos that are capable of germinating to yield conifer plants. Preferably conifer somatic embryos, formed in vitro, are physically and physiologically similar, or identical, to conifer zygotic embryos formed in vivo in conifer, seeds. A particular problem affecting conifer somatic embryogenesis is the asynchronous development of somatic embryos from cultures of embryogenic cells. This asynchrony in development results in cultures in which embryos are at disparate stages of development, greatly reducing the overall efficiency of the process. There is therefore a continuing need for methods for producing conifer somatic embryos from conifer embryogenic cells. The present invention provides methods that satisfy this need.